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Diffstat (limited to 'source/blender/gpu/shaders/compositor/compositor_screen_lens_distortion.glsl')
-rw-r--r-- | source/blender/gpu/shaders/compositor/compositor_screen_lens_distortion.glsl | 151 |
1 files changed, 151 insertions, 0 deletions
diff --git a/source/blender/gpu/shaders/compositor/compositor_screen_lens_distortion.glsl b/source/blender/gpu/shaders/compositor/compositor_screen_lens_distortion.glsl new file mode 100644 index 00000000000..dc572ea5aaf --- /dev/null +++ b/source/blender/gpu/shaders/compositor/compositor_screen_lens_distortion.glsl @@ -0,0 +1,151 @@ +#pragma BLENDER_REQUIRE(gpu_shader_common_hash.glsl) +#pragma BLENDER_REQUIRE(gpu_shader_compositor_texture_utilities.glsl) + +/* A model that approximates lens distortion parameterized by a distortion parameter and dependent + * on the squared distance to the center of the image. The distorted pixel is then computed as the + * scalar multiplication of the pixel coordinates with the value returned by this model. See the + * compute_distorted_uv function for more details. */ +float compute_distortion_scale(float distortion, float distance_squared) +{ + return 1.0 / (1.0 + sqrt(max(0.0, 1.0 - distortion * distance_squared))); +} + +/* A vectorized version of compute_distortion_scale that is applied on the chromatic distortion + * parameters passed to the shader. */ +vec3 compute_chromatic_distortion_scale(float distance_squared) +{ + return 1.0 / (1.0 + sqrt(max(vec3(0.0), 1.0 - chromatic_distortion * distance_squared))); +} + +/* Compute the image coordinates after distortion by the given distortion scale computed by the + * compute_distortion_scale function. Note that the function expects centered normalized UV + * coordinates but outputs non-centered image coordinates. */ +vec2 compute_distorted_uv(vec2 uv, float scale) +{ + return (uv * scale + 0.5) * texture_size(input_tx) - 0.5; +} + +/* Compute the number of integration steps that should be used to approximate the distorted pixel + * using a heuristic, see the compute_number_of_steps function for more details. The numbers of + * steps is proportional to the number of pixels spanned by the distortion amount. For jitter + * distortion, the square root of the distortion amount plus 1 is used with a minimum of 2 steps. + * For non-jitter distortion, the distortion amount plus 1 is used as the number of steps */ +int compute_number_of_integration_steps_heuristic(float distortion) +{ +#if defined(JITTER) + return distortion < 4.0 ? 2 : int(sqrt(distortion + 1.0)); +#else + return int(distortion + 1.0); +#endif +} + +/* Compute the number of integration steps that should be used to compute each channel of the + * distorted pixel. Each of the channels are distorted by their respective chromatic distortion + * amount, then the amount of distortion between each two consecutive channels is computed, this + * amount is then used to heuristically infer the number of needed integration steps, see the + * integrate_distortion function for more information. */ +ivec3 compute_number_of_integration_steps(vec2 uv, float distance_squared) +{ + /* Distort each channel by its respective chromatic distortion amount. */ + vec3 distortion_scale = compute_chromatic_distortion_scale(distance_squared); + vec2 distorted_uv_red = compute_distorted_uv(uv, distortion_scale.r); + vec2 distorted_uv_green = compute_distorted_uv(uv, distortion_scale.g); + vec2 distorted_uv_blue = compute_distorted_uv(uv, distortion_scale.b); + + /* Infer the number of needed integration steps to compute the distorted red channel starting + * from the green channel. */ + float distortion_red = distance(distorted_uv_red, distorted_uv_green); + int steps_red = compute_number_of_integration_steps_heuristic(distortion_red); + + /* Infer the number of needed integration steps to compute the distorted blue channel starting + * from the green channel. */ + float distortion_blue = distance(distorted_uv_green, distorted_uv_blue); + int steps_blue = compute_number_of_integration_steps_heuristic(distortion_blue); + + /* The number of integration steps used to compute the green channel is the sum of both the red + * and the blue channel steps because it is computed once with each of them. */ + return ivec3(steps_red, steps_red + steps_blue, steps_blue); +} + +/* Returns a random jitter amount, which is essentially a random value in the [0, 1] range. If + * jitter is not enabled, return a constant 0.5 value instead. */ +float get_jitter(int seed) +{ +#if defined(JITTER) + return hash_uint3_to_float(gl_GlobalInvocationID.x, gl_GlobalInvocationID.y, seed); +#else + return 0.5; +#endif +} + +/* Each color channel may have a different distortion with the guarantee that the red will have the + * lowest distortion while the blue will have the highest one. If each channel is distorted + * independently, the image will look disintegrated, with each channel seemingly merely shifted. + * Consequently, the distorted pixels needs to be computed by integrating along the path of change + * of distortion starting from one channel to another. For instance, to compute the distorted red + * from the distorted green, we accumulate the color of the distorted pixel starting from the + * distortion of the red, taking small steps until we reach the distortion of the green. The pixel + * color is weighted such that it is maximum at the start distortion and zero at the end distortion + * in an arithmetic progression. The integration steps can be augmented with random values to + * simulate lens jitter. Finally, it should be noted that this function integrates both the start + * and end channels in reverse directions for more efficient computation. */ +vec3 integrate_distortion(int start, int end, float distance_squared, vec2 uv, int steps) +{ + vec3 accumulated_color = vec3(0.0); + float distortion_amount = chromatic_distortion[end] - chromatic_distortion[start]; + for (int i = 0; i < steps; i++) { + /* The increment will be in the [0, 1) range across iterations. */ + float increment = (i + get_jitter(i)) / steps; + float distortion = chromatic_distortion[start] + increment * distortion_amount; + float distortion_scale = compute_distortion_scale(distortion, distance_squared); + + /* Sample the color at the distorted coordinates and accumulate it weighted by the increment + * value for both the start and end channels. */ + vec2 distorted_uv = compute_distorted_uv(uv, distortion_scale); + vec4 color = texture(input_tx, distorted_uv / texture_size(input_tx)); + accumulated_color[start] += (1.0 - increment) * color[start]; + accumulated_color[end] += increment * color[end]; + } + return accumulated_color; +} + +void main() +{ + ivec2 texel = ivec2(gl_GlobalInvocationID.xy); + + /* Compute the UV image coordinates in the range [-1, 1] as well as the squared distance to the + * center of the image, which is at (0, 0) in the UV coordinates. */ + vec2 center = texture_size(input_tx) / 2.0; + vec2 uv = scale * (texel + 0.5 - center) / center; + float distance_squared = dot(uv, uv); + + /* If any of the color channels will get distorted outside of the screen beyond what is possible, + * write a zero transparent color and return. */ + if (any(greaterThan(chromatic_distortion * distance_squared, vec3(1.0)))) { + imageStore(output_img, texel, vec4(0.0)); + return; + } + + /* Compute the number of integration steps that should be used to compute each channel of the + * distorted pixel. */ + ivec3 number_of_steps = compute_number_of_integration_steps(uv, distance_squared); + + /* Integrate the distortion of the red and green, then the green and blue channels. That means + * the green will be integrated twice, but this is accounted for in the number of steps which the + * color will later be divided by. See the compute_number_of_integration_steps function for more + * details. */ + vec3 color = vec3(0.0); + color += integrate_distortion(0, 1, distance_squared, uv, number_of_steps.r); + color += integrate_distortion(1, 2, distance_squared, uv, number_of_steps.b); + + /* The integration above performed weighted accumulation, and thus the color needs to be divided + * by the sum of the weights. Assuming no jitter, the weights are generated as an arithmetic + * progression starting from (0.5 / n) to ((n - 0.5) / n) for n terms. The sum of an arithmetic + * progression can be computed as (n * (start + end) / 2), which when subsisting the start and + * end reduces to (n / 2). So the color should be multiplied by 2 / n. The jitter sequence + * approximately sums to the same value because it is a uniform random value whose mean value is + * 0.5, so the expression doesn't change regardless of jitter. */ + color *= 2.0 / vec3(number_of_steps); + + imageStore(output_img, texel, vec4(color, 1.0)); +} |